The present invention is related to the devices disclosed in U.S. Pat. No. 6,743,358 and U.S. Pat. No. 7,807,059.
U.S. Pat. No. 6,743,358 relates to apparatus for collecting material floating on the surface of a body of water. The apparatus according can be used for collecting different kinds of pollutants, both solid and liquid, floating on the water, but it is particularly devised and suited for collecting oil spilled on a water surface, including oil mixed with solid material. More particularly, the apparatus relates to a skimmer apparatus (skimmer) of the kind adapted to skim a surface layer across a skinning weir of an immersed collection vessel and allow the pollutants to accumulate on the surface of the water in the collection vessel so that they can then be removed in some suitable manner.
WO97/07292 and WO99/22078 disclose prior art embodiments of apparatus of that kind. In this kind of prior art apparatus the collection vessel has a side wall comprising an upper wall part which has some buoyancy and the upper end of which forms the skimming weir, and a lower wall part, the upper wall part being vertically movable relative to the lower wall part. The upper and lower wall parts jointly delimit laterally an upper subcompartment of a collection compartment having an inlet that is formed by the skimming weir. A lower subcompartment of the collection compartment forms an extension of and is in open communication with the upper subcompartment. Water can be fed into and discharged from the collection vessel through an opening in a bottom wall thereof.
In the apparatus disclosed in WO97/07292 the oil is collected on the surface of the water accommodated in the upper subcompartment of the collection compartment. It is discharged from the collection compartment by feeding water from below into the collection compartment to cause the skimming weir to be pressed against an overlying plate having a discharge opening and cause the oil layer on the water surface to be expelled through the discharge opening into a suitable recipient.
In the apparatus disclosed in WO99/22078, the oil is accumulated in a separation compartment that is delimited laterally between a inner wall, which resembles the side wall of the apparatus according to WO97/07292, and an outer wall. The oil enters across the skimming weir of the inner wall and moves downward in the collection compartment delimited by the inner wall. At the lower edge of the inner wall the oil enters the separation compartment where it accumulates on the surface of the water therein. The separation compartment is delimited upward by a top wall with a discharge opening through which the oil can be expelled in the same manner as in the apparatus according to WO97/07292 by feeding water from below into the collection vessel.
An advantage of positioning the separation compartment outside the collection compartment delimited by the inner wall is that the oil flowing outward from that compartment into the separation compartment is distributed horizontally over an area that can readily be made much larger than the horizontal area delimited by the inner wall. Accordingly, the horizontal velocity of the oil in the separation compartment can be very low, thereby allowing the oil to rise substantially without disturbance to the surface in the separation compartment.
Solid objects of various kinds are often carried along by the oil and cause problems when the oil is to be discharged from the separation compartment. In the apparatus according to WO99/22078, such objects have a tendency to collect at the top of the layer of oil in the separation compartment, adjacent the top wall or roof of the collection compartment, and to remain there when the oil is expelled through the discharge opening. As a result, only those objects which are below or close to the discharge opening are carried along with the oil discharged from the separation compartment.
The apparatus according to U.S. Pat. No. 6,743,358 is adapted to float in the body of water carrying the material of lower density to be collected. This material is herein supposed to be oil, possibly mixed with solid objects of one kind or another, such as bottle caps, pieces of plastic, pieces of bark and wood, or other debris. It should be noted, however, that the invention is also advantageously useful for collecting exclusively solid debris, such as leaves or other plant debris floating on the water surface in open-air pools.
A known method for collecting pollutants having a density higher than that of water and carried by a surface layer of a body of water uses a skimmer apparatus, that is, an apparatus by which the surface layer of the body of water is skimmed off into a collection vessel. An example is shown in WO01/12905 A1.
The method is cyclical with each cycle of operation comprising an intake phase and a discharge phase. During the intake phase, the surface layer runs into a collection vessel having a separation compartment with a top wall. The inflow into the collection vessel takes place through an inlet that communicated with the separation compartment. During the intake phase the pollutants entrained by the inflowing surface layer are allowed to collect gravimetrically, that is, by virtue of their lower density, as a layer of pollutants beneath the top wall of the separation compartment. This layer floats on the underlying water in the separation compartment.
During the discharge phase, the layer of pollutants collected beneath the top wall of the separation compartment is dispelled from the separation compartment through a riser outlet by introducing water as a displacing liquid into the separation compartment beneath the layer of pollutants.
As actually used, the skimmer apparatus by means of which the method is implemented operates automatically, the intake and discharge phases being initiated and terminated under control based on sensing the interfaces between the pollutant and water layers in the separation compartment and the riser outlet. According to WO01/12905 A1, the sensing is carried out using ultrasonic sensors, but other types of sensors may also be used. In order that the collection may take place efficiently, the control of the intake and discharge phases must be controlled in a reliable manner and include a possibility to simple adaptation to the conditions existing in each case, such as the amount of heavier particles which are carried by the skimmed surface layer into the collection vessel and settle therein, the composition and viscosity of the pollutants, etc. The pollutants often comprise a mixture of solid and liquid pollutants and may partially have a density higher than that of the water in the skimmed surface layer and partially have a lower density than the water.
Using conventional sensors it is difficult to control the intake and discharge phases reliably in a satisfactory manner. Ultrasonic sensors, for example, may operate in an excellent manner if they are properly set for the layers on which the sound is to be reflected or which the sound is to penetrate, but if the density or sonic transmission properties of the layer should change, the setting of the sensor has to be changed. If particles enter the region of the sensors, the function is affected in an unpredictable manner.
Other sensors which may be contemplated for the detection of the interfaces or density differences between the layer of pollutants and the water carrying the layer suffer for diverse problems which make it difficult to have a satisfactory control of the intake and the discharge in all operating situations.
A further problem is caused by the fact that the skimmed surface layer often contains material that has a higher density than the water of the surface layer but is nevertheless entrained by the surface layer and carried into the collection vessel. In the collection vessel, however, this material may settle because of the low flow velocities which exist, especially in the separation compartment. The settled material may collect on the bottom wall of the separation compartment and gradually load the collection vessel heavily enough to jeopardize the function of the skimmer apparatus.
The problem to be solved by U.S. Pat. No. 7,807,059 is to provide a method of the kind indicated in which the initiation and termination of the intake and discharge phases can be controlled reliably in a satisfactory manner.
In accordance with U.S. Pat. No. 7,807,059, the solution to this problem is based on monitoring the changes of the weight of the collection vessel in the body of water during the operating cycle and initiating the intake and discharge phases in response to the said weight reaching predetermined values. These changes can be monitored in different ways.
One way is to measure the distance between the surface of the body of water and reference point which is fixed relative to the collection vessel and situated above the surface of the body of water. The changes manifest themselves by changes in the depth of immersion of the collection vessel. The distance measurement can be carried out using an echo sounder, for example.
Another way is to directly measure the weight of the collection vessel in the body of water using a load cell.
U.S. Pat. No. 7,807,059 also relates to apparatus for the implementation of the method according to the invention and to a software product which is especially for use in carrying out the method according to U.S. Pat. No. 7,807,059 using a computer and auxiliary means coacting with it. Use of this software product may take place exclusively locally in the collection apparatus using a computer installed therein or via a communication link using a server which is geographically separated from the collection apparatus, such as a server which can be accessed via the Internet.
Thus, the present invention is related to the devices disclosed in U.S. Pat. No. 6,743,358 and U.S. Pat. No. 7,807,059 B2.
The apparatuses disclosed in those patents may be described as skimming and separation apparatus that can be used for collecting different kinds of pollutants, both solid and liquid; floating on the water, but it is particularly devised and suited for collecting oil spilled on a water surface, including oil mixed with solid material. They comprise of a separation and collecting vessel. The collecting compartment includes an upper sub compartment delimited laterally by an inner wall having a skimming weir device forming an inlet to the collection compartment and a lower sub-compartment which is delimited laterally by an outer wall and communicates with a separation and storage compartment and to a bottom outlet. The separation and storage compartment is in its peripheral connection to an outflow compartment with driving means for discharging water there from through a bottom outlet. The inner wall (collecting strut) and the outer wall (outer casing) that generates the separation and storage compartment can accumulate and store floating material. This compartment is in open communication with the inner sub-compartment of the collection compartment. A valve is provided at the top of the separation compartment and when in open position connects the separation compartments with the upper sub compartment of the collection compartment. The valve stays in a closed position during the collection of pollutants due to the under pressure that is generated by the bottom discharge means during the collecting phase. Once the separating and storage compartment is considered to be full enough an emptying phase starts by reversing the flow through the apparatus. The outlet will now become the inlet and pressure will be generated inside the apparatus. The valve will open and the weir skimming device will close to a derbies outlet arrangement.
The collected and stored pollutants in the separating and storage compartment are now supposed to by its flotation forces migrate over to the upper sub compartment of the collection compartment. Once the pollutants is in place hydraulic forces, generated by the bottom driving means will force the pollutants be expelled through the pollution outflow into disposable floating bags or other storing means.
It has been found out that the separation of the above mentioned devices is very good, but that it is very difficult and time consuming to empty the device when high viscosity oils and mixed pollutants are collected.
One object of the present invention is to achieve an improved skimming and separation apparatus that is easier and less time consuming to empty than previously known apparatus, in particular when high viscosity oils and mixed pollutants are collected.
Another object of the present invention is to achieve an improved separation device that is configured for use in a wide range of applications and modes.